Seesaw Neutrino Signals at the Large Hadron Collider

TL;DR

This paper explores how five-dimensional models can make the seesaw mechanism for tiny neutrino masses observable at the LHC, focusing on tri-lepton signals with missing energy.

Contribution

It demonstrates that the seesaw mechanism can be tested at colliders within a five-dimensional framework, reconciling large couplings with tiny neutrino masses.

Findings

Observable tri-lepton signals at the LHC are possible.

The model can distinguish between different neutrino mass spectra.

Collider signals can reveal extra dimensions and neutrino mass origins.

Abstract

We discuss the scenario with gauge singlet fermions (right-handed neutrinos) accessible at the energy of the Large Hadron Collider. The singlet fermions generate tiny neutrino masses via the seesaw mechanism and also have sizable couplings to the standard-model particles. We demonstrate that these two facts, which are naively not satisfied simultaneously, are reconciled in the five-dimensional framework in various fashions, which make the seesaw mechanism observable. The collider signal of tri-lepton final states with transverse missing energy is investigated for two explicit examples of the observable seesaw, taking account of three types of neutrino mass spectrum and the constraint from lepton flavor violation. We find by showing the significance of signal discovery that the collider experiment has a potential to find signals of extra dimensions and the origin of small neutrino masses.